minitest/unit is meant to have a clean implementation for language
implementors that need a minimal set of methods to bootstrap a working
test suite. For example, there is no magic involved for test-case
discovery.

Log message:
* Support ruby200, ruby21 and ruby22 since ruby23 bundles the same version
of minitest gem.
No bump PKGREVISION since it has already broken with ruby23 and other
versions are not affected.